The use of trusses in building light-weight structures to withstand large loads has become common. These light-weight trusses, at an early date were constructed with metal chords connected by metal bars or tubular pipes with flattened ends. Early examples of metal bars with flattened ends are the Mansfield towers for supporting electric transmission cables; U.S. Ser. No. 849,908, Apr. 9, 1907; and the Wooldridge floor truss U.S. Pat. No. 1,813,373, July 7, 1931. A major weak point in the design of these trusses was the flattened ends of the webs which failed by buckling.
In the early 1960's, particularly in the Western states, a "composite truss" came into wide usage. These trusses used the abundant supply of western wood in the chords and "borrowed" the tubular metal webs with flattened ends from the all-steel trusses used in the Eastern United States. (See the Troutner composite truss, U.S. Pat. No. 3,137,899, June 23, 1964). These trusses had a single upper and a single lower wood member. Since the connection between the metal pin and the wood chord of the Troutner composite truss was the weakest link the the truss, the use of the tubular web members with the weakened flattened ends was of secondary concern.
A major breakthrough in composite trusses was accomplished by Gilb ten years later, by locating the metal pin on the edge of the single wood chord instead of within the wood chord. This eliminated the wood splitting problem and the metal connector raised the load values in the joint considerably, but the weakest point in the truss design was the flattened end of the metal webs. Gilb was granted U.S. Pat. No. 3,857,218, Dec. 31, 1974.
Because the flattened web end was the limiting factor in the Gilb edge pin connector truss, tubing of heavier gauge than would otherwise be required was used. Gilb recognized the problem of the flattened web end and in 1973 designed webs with different end configurations in which the tube bulge on one side continued down to the edge of the hole, while on the other side, the edge of the bulge was restrained to its normal position so that a flat area 11/2 inches in diameter concentric with the hole was available for attachment and insert. Because of the shape of the web ends, this project was dubbed "The Dolphin Project." Due to faulty testing procedures, the webs collapsed at low design loads and the project was aborted.
At about the same time, a separate project was run dealing with the separate problem of improving the bearing of the web on the pin. With a drilled or punched hole, this was limited to the value of the metal-to-metal contact area. The obvious improvement was tried by drawing the holes to provide increased metal-to-metal bearing area, but this project too was abandoned when it was found that the drawn hole merely caused the flat area of the web to buckle at a lower value.